We now assume that we have an accurate model of the state, and we've
received some sensory input from the simulator for the next time step.
We have to update our model to account for this input. We divide this
update into two stages depending on what caused the changes to the
model. First, we update the model for internal changes, those that are
caused by the client (e.g. turning and dashing have a large impact on
the model since the positions that are stored are relative to the
client.) Second, we update the model for external changes, those that
are not directly caused by the client (e.g. the motion of the ball and
other clients.)